The present invention relates to an information-signal playback system, an information-signal reading apparatus, an information-signal processing apparatus, an information-signal playback method, an information-signal reading method and an information-signal processing method for protecting the copyright of an information signal recorded on recording media such as a DVD (Digital Video Disc) for presenting the information signal to the user or an information signal transmitted through transmission media such as the Internet and for preventing an illegal copy of such an information signal from being produced.
With popularization of digital contents transmitted through the Internet and recorded on a digital video disc going on in recent years, infringement of a copyright granted to authors of digital contents in the form of an illegal copy of the digital contents becomes a problem. In order to solve the problem, there is a conceivable technique for preventing an illegal copy of digital contents from being produced. The technique uses information added to the digital contents for controlling copies of the digital contents.
With regard to prevention of an illegal copy from being produced, one can conceive a control implementation whereby a copy is not allowed at all and another control implementation in which a copy produced from an original source is allowed, but not of a copy produced from a copy in dependence on a source on which the copy prevention control is to be implemented. The latter is also referred to as a generation-limited copy control system. The former is applied to original software produced and sold by a content maker such as contents of a DVD-ROM. On the other hand, the generation-limited copy control system is applied to, among others, information transmitted through broadcasting media.
In the case of the generation-limited copy control system, a system capable of controlling copy generations is desirable. As a system of information on copy control capable of controlling copy generations, there have been proposed a CGMS (Copy Generation Management System) and a system using digital-watermark processing.
The digital-watermark processing is processing to embed information as noise into a part of picture data or music data which is trivial to the perception of a human being or a non-redundant part of a piece of music or a picture. Additional information embedded in such digital-watermark processing into picture or music data is difficult to extract from the data. On the other hand, it is possible to detect additional information embedded in such digital-watermark processing into picture or music data from the data even after the data has been subjected to a filtering process or data compression.
In the case of a copy control system using digital-watermark processing, additional information to be embedded into picture or music data indicates one of the following 4 control implementations:
(1) Copy Free (allowing copies to be produced freely)
(2) One Copy (allowing only the first copy generation to be produced)
(3) No More Copy (allowing no subsequent copy generations)
(4) Never Copy (absolutely allowing no copy)
The above control implementations represent restrictions of copy generations and copies of the picture or music data on which information is superposed by the digital-watermark processing.
In the copy-free control implementation, music or picture data can be copied freely. In the one-copy control implementation, only the first copy generation of music or picture data can be produced. The no-more-copy control implementation is applied to music or picture data of the first copy generation which has been produced in compliance with the one-copy control implementation (the second control implementation). With the no-more-copy control implementation, music or picture data of the first copy generation is prohibited from copying. The never-copy control implementation (the fourth control implementation) does not allow a copy to be produced at all.
If digital-watermark information superposed on picture or music data indicates the one-copy control implementation, a recording apparatus conforming digital-watermark processing (that is conforming to copy-restriction processing) will find out that the picture or music data can be copied and recorded, and thus record a copy of the data. However, the recording apparatus will update the digital-watermark information to information indicating the no-more-copy control implementation and superpose the updated information on the recorded data. If digital-watermark information superposed on picture or music data to be dubbed indicates the no-more-copy control implementation, on the other hand, a recording apparatus conforming digital-watermark processing will determine that an operation to copy and record the picture or music data thereof is prohibited and inhibit a recording operation.
The CGMS system is a system in which 2-bit additional information for copy control is superposed on 1 specific horizontal zone in a vertical blanking period if the picture signal is an analog signal, or 2-bit additional information is added to picture data if the picture data is digital data.
The 2-bit information added by the CGMS system which is referred to hereafter as CGMS information has the following meanings:
[00]—Copy-free control implementation
[10]—One-copy control implementation (allowing one-generation copy)
[11]—Never-copy control implementation (copy strictly prohibited)
The CGMS system does not implement the no-more-copy control implementation described above.
If the CGMS information added to picture data is [10], a recording apparatus conforming to the CGMS system will find out that the picture data can be copied and recorded and record a copy of the data. However, the recording apparatus will update the CGMS information to [11] and superpose the updated information on the recorded data. If CGMS information superposed on picture data to be recorded is [11], on the other hand, a recording apparatus conforming to the CGMS system will determine that an operation to copy and record the picture data thereof is prohibited and inhibit a recording operation.
By the way, in a recording apparatus not implementing copy control based on information on copy control such as CGMS information or digital-watermark information, for example, an input main information signal can be copied in some cases even if the input main information signal includes additional information on copy control indicating the never-copy or one-copy control implementation.
In order to solve the aforementioned problem, in addition to the digital-watermark and CGMS information described above, information on copyright protection is recorded into a recording medium for recording a main information signal including picture or music data. One can conceive that, by using information on copyright protection, a person committing an illegal copy act can be investigated with ease and can be proven easily, and the use of an illegally copied main information signal can be invalid.
Examples of the information on copyright protection are information identifying an author creating the main information signal, various kinds of information useful for proving, investigating or exposure of an illegal copying act and information restricting the use of a main information signal. The information identifying an author includes the name or a code of the author. The information useful for proving, investigating or exposure of an illegal copying act includes a date on which a main information signal is recorded into a recording medium or data for identifying a recording apparatus. The information restricting the use of a main signal includes information indicating a valid period during which the user is allowed to use the main information signal and the serial number of an apparatus for playing back the main information signal.
In addition, in the case of a disc recording medium, in order to allow a playback or recording apparatus to distinguish a read-only ROM disc or a rewritable RAM disc from each other, medium-type identification information is recorded typically in a TOC (Table of Contents) or a directory of the disc. The medium-type identification information is also used as information on copyright protection. For example, by using the medium-type identification information in conjunction with digital-watermark information described above, it is possible to inhibit an operation to play back a main information signal obtained as a result of an illegal copy operation.
This is because there will be a difference in information on copy control added to a main information signal recorded on a recording medium between an unrewritable read-only ROM disc legally containing a main information signal such as picture data presented by a content maker and a rewritable RAM disc containing information obtained as a result of an operation to copy a main information signal which is originally recorded on such a ROM disc and presented to the user through communication media such as the Internet.
That is to say, in the case of the so-called commercially available ROM disc, digital-watermark information indicating a never-copy control implementation is normally added to a main information signal recorded on the ROM disc in order to protect the disc from an operation to illegally copy the signal.
In the case of a RAM disc used by the user mainly for recording a main information signal, on the other hand, digital-watermark information indicating a never-copy or a one-copy control implementation is never added to the main information signal recorded on the disc.
That is to say, digital-watermark information which shows a never-copy control implementation and is added to a main information signal recorded on a RAM disc indicates that the main information signal has been obtained as a result of an operation to illegally copy a main information signal recorded on a ROM disc implementing the never-copy control.
In addition, when digital-watermark information which shows a one-copy control implementation added to a main information signal recorded on a RAM disc is rewritten by an apparatus implementing copy control based on information on copy control into a no-more-copy control implementation and the main information signal with this digital-watermark information indicating the no-more-copy control implementation is then recorded into the RAM disc. Thus, a main information signal recorded on a RAM disc will not eventually have digital-watermark information indicating a one-copy control implementation. If such a RAM disc exists, the main information signal recorded therein must have been obtained as a result of an illegal copy operation.
In addition, even though a main information signal recorded normally on a ROM disc may have additional digital-watermark information indicating a never-copy control implementation, the main information signal is never rewritten into a ROM disc. Thus, there is no way that a main information signal recorded on a ROM disc has additional digital-watermark information indicating a no-more-copy control implementation.
It should be noted that additional information indicating a one-copy control implementation for a main information signal recorded on a ROM disc allows a first-generation copy of the main information signal to be produced from the ROM disc. The permission to generate a first-generation copy also means that a copy of the main information signal can always be produced as long as the copy is made from the same ROM disc as an original source and also means that, as a matter of fact, the main information signal can be copied from the ROM disc with a high degree of freedom. The presentation of a main information signal in such a way is not conceived as a desirable presentation from the copyright-protection point of view. Nevertheless, the fact that the use of additional information indicating a one-copy control implementation for a main information signal recorded on a ROM disc is not prohibited means that the presentation of a main information signal in such a way may exist.
In order to take advantage of the fact that a difference in information on copy control added to a main control signal recorded on a recording medium exists between a ROM disc and a RAM disc as described above, there has been conceived a disc playback apparatus shown in FIG. 8 wherein control to play back a main information signal from a disc such as a DVD is executed by using media identification information of the disc in conjunction with information on copy control such as the digital-watermark information added to the main information signal. The media identification information is also referred to hereafter as information on the media type. The conceivable disc playback apparatus of this type is explained as follows.
As shown in FIG. 8, an information-signal playback apparatus (an information-signal playback system) 100 comprises a disc playback apparatus 101, a data processing unit 102 and a transmission line 103 connecting the disc playback apparatus 101 and the data processing unit 102. In this system, the disc playback apparatus 101 is implemented typically by a disc drive apparatus for reading out a main information signal from a disc such as a DVD. On the other hand, the data processing unit 102 is a personal computer for carrying out predetermined processing on a main information signal read out by the disc playback apparatus 101 from a disc and for outputting a result of the processing.
A disc 300, on which a main information signal to be played back has been recorded, is mounted on the disc playback apparatus 101. Then, a readout unit 104 employed in the disc playback apparatus 101 reads out the main information signal recorded in a data area of the disc 300 and information on the media type recorded typically in a TOC of the disc 300. The information on the media type is then supplied to a media-type decoding unit 105 employed in the data processing unit 102 through the transmission line 103 and the main information signal is supplied to a digital-watermark-information detecting unit 106 and a switch circuit 108 also employed in the data processing unit 102 through the transmission line 103.
The media-type decoding unit 105 decodes the information on the media type, outputting information indicating whether the disc 300 mounted on the disc playback apparatus 101 is a RAM or ROM disc to an output control unit 107. On the other hand, the digital-watermark-information detecting unit 106 detects the information on copy control superposed on the main information signal as digital-watermark information, outputting the information on copy control also to the output control unit 107.
The output control unit 107 controls a switch circuit 108 to turn on or off in accordance with the information indicating the media type and the information on copy control. To put it in detail, if the disc 300 is a ROM disc with the information on copy control indicating a no-more-copy control implementation or if the disc 300 is a RAM disc with the information on copy control indicating a never-copy or one-copy control implementation, the output control unit 107 determines that the main information signal recorded on the disc 300 is an illegal copy as described above. In this case, the output control unit 107 executes control to turn off the switch circuit 108, disallowing the main information signal to be supplied to any apparatus at the following stage. Otherwise, the output control unit 107 determines that the main information signal recorded on the disc 300 is legally produced, executing control to turn on the switch circuit 108.
In this way, by referring to the information on the media type of a disc containing a recorded main information signal to be played back, the information-signal playback system 100 is capable of preventing a main information signal illegally recorded on the disc from being played back.
If the information on the media type of the disc is improperly altered during transmission between the disc playback apparatus 101 and the data processing unit 102, however, a main information signal illegally recorded on the disc can be played back and manipulated illegally. As a result, there is raised a problem of repeated illegal copy operations. Assume that a main information signal recorded on a ROM disc with additional digital-watermark information indicating the never-copy control implementation is illegally copied into a RAM disc which normally never includes information on copy control indicating a never-copy control implementation. Since the RAM disc illegally copied the contents of the ROM disc, however, there are some cases where the main information signal copied into the RAM disc has the additional digital-watermark information indicating the never-copy control implementation.
In such a case, the information-signal playback system 100 shown in FIG. 8 will not play back the main information signal illegally copied into the RAM disc provided that the playback control described above is executed normally. With an illegal playback system 200 shown in FIG. 9, however, a main information signal obtained as a result of an illegal copy operation can be played back and manipulated with a high degree of freedom as described below.
A media-type altering apparatus 201 shown in FIG. 9 is used for altering information on the media type read out from a disc by the readout unit 104 employed in the disc playback apparatus 101 to information indicating another media type. To be more specific, the media-type altering apparatus 201 alters information on the media type read out from the disc by the readout unit 104 to other media-type information indicating a ROM disc, if the information read out indicates a RAM disc, or to other media-type information indicating a RAM disc if the information indicates a ROM disc. Then, the media-type altering apparatus 201 supplies the altered information on the media type to the media-type decoding unit 105 employed in the data processing unit 102.
When a RAM disc is illegally recorded a main information signal with additional digital-watermark information indicating the never-copy control implementation by means of a ROM disc or indicating the never-copy or one-copy control implementation by the way of the Internet, the illegal playback system shown in FIG. 9 is capable of normally playing back a main information signal presented to the user along with additional digital-watermark information indicating the never-copy control implementation or presented to the user along with additional digital-watermark information indicating the never-copy or one-copy control implementation by the way of the Internet. Accordingly, even a main information signal obtained as a result of an illegal copy operation of the signal into a RAM disc can be utilized. In this case, the copyright is infringed by the use of the illegal main information signal.
Such infringement of a copyright is made possible by alteration of not only information on the media type but also other information on copyright protection such as information indicating a valid period during which the user is allowed to play back a main information and information restricting usable playback apparatuses. That is to say, with these other pieces of information on copyright protection altered after being read out from a disk, control of an operation to play back a main information signal can no longer be executed normally. Also in this case, a main information signal obtained as a result of an illegal copy operation or a main information signal with restricted playback operations can be reproduced without restrictions and the author of the main information signal loses many benefits, to which the author is entitled.